Updating C: removing non standard header file

[AllCodeBreaker]

Removing non standard header file <conio.h>

<conio.h> header file has never been a part of standard C, but the cheatsheet contains it. It is not supported by modern standards like C99 or later. Remove the header file as well as the functions like getch(), clrscr(), etc

Issue at C.md file

Occurrence sections

Read the file: fgetc()
Write to file: fputs()
Read files: fgets()
rewind()
ftell()